1. Field of the Invention
The present invention relates to a multi-cylinder internal combustion engine in which throttle valves disposed in air-intake channels formed independently for each cylinder are opened and closed by an electric motor.
2. Description of Background Art
A multi-cylinder internal combustion engine is known wherein throttle valves are opened and closed by an electric motor, for example, see JP-A-2002-256895. The four-cylinder internal combustion engine includes throttle valves provided for each cylinder. The four throttle valves are opened and closed by a single drive motor or are divided into two groups each having two throttle valves with the two throttle valves in each group being opened and closed by a single drive motor.
In the related art, a plurality of throttle valves are driven by a single drive motor. Thus, the output control for each cylinder cannot be performed. Therefore, it is difficult to control the output of the multi-cylinder internal combustion engine in various ways depending on the state of usage of the object to be driven, such as a vehicle. For example, in a variable cylinder internal combustion engine in which the operating state can be switched between a full cylinder operation in which all the cylinders are activated and a partial cylinder operation in which part of the cylinders come to halt, it is necessary to control the opening of each throttle valve in each cylinder in order to reduce torque disalignment in association with the switching of the operating state. However, in the related art described above, it is difficult to perform the output control for each cylinder to satisfy such requirement. Since a plurality of throttle valves are grouped into one set, the arrangement or the number of cylinders to which the throttle valves to be driven by the drive motor are applied is limited, and hence the multi-cylinder internal combustion engine, to which shared components are applied, is limited. In addition, there is a problem as to how an opening sensor for detecting the opening of the throttle valve, which is necessary for driving the throttle valve by the drive motor, can be compactly arranged.